Since the prediction of the Dyakonov-Shur plasma instability in the current-driven two-dimensional electron channels of the field-effect transistor structures leading to
the terahertz (THz) emission [1]}, [2]}, such an emission have been
extensively discussed in the literature (see, for example, [3]}, [4]}, [5]}, [6]}, [7]}, [8]}, [9]}, [10]}, [11]}, [12]}, [13]}, [14]}, [15]} and the references therein).
As demonstrated recently [16]}, [17]}, [18]}, the Coulomb electron drag [19]}, [20]}, [21]}, [22]}, [23]} by the injected hot electrons or/and holes
in the graphene layer (GL) n-i-n and p-i-n structures [1]}, [2]}, [15]}, [27]}, [28]} (see also [29]}),
could enable a specific instability mechanism. In these structures, the gated regions play the role of the plasmonic resonant cavities.
The finite transit time of the holes and electrons injected or generated in the depleted regions of the GL channel can enable the negative dynamic conductivity on the order of the inverse
transit time [30]}, [31]}.
